JAVA EE: byName Auto-Wiring

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Monday, 16 July 2018

What is byName Auto-wiring mode in Spring?

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Introduction

In the Spring Framework, auto-wiring simplifies XML configuration by allowing the Spring container to automatically inject collaborating beans into properties. In byName auto-wiring mode (autowire="byName"), Spring inspects the bean's property names and searches the XML configuration for a bean whose id matches the property name exactly.

How Does byName Auto-Wiring Work?

Property Name Matching: Spring looks at the property name (derived from setter methods like setAddress(...) → address).
Bean ID Lookup: Spring searches the application context for a bean definition with an id or name identical to that property name.
Automatic Injection: When a match is found, Spring calls the corresponding setter method to inject the dependency without requiring manual <property ref="..."/> tags.
Graceful Fallback: If no bean with a matching ID exists in the container, Spring leaves the property un-set (null) without throwing an error.

Step-by-Step Configuration Example

Consider an Employee class that has an address property:

1. The Java Model Class

package com.ram.model;

public class Employee {
    private Address address;

    // Setter method used by byName autowiring
    public void setAddress(Address address) {
        this.address = address;
    }

    public void display() {
        System.out.println("Employee Address: " + address);
    }
}

2. Configuring autowire="byName" in applicationContext.xml

Notice how the bean ID address matches the property name inside Employee:

<!-- Bean ID matches the property name 'address' -->
<bean id="address" class="com.ram.model.Address">
    <property name="city" value="Bangalore" />
    <property name="state" value="Karnataka" />
</bean>

<!-- Employee bean with autowire="byName" -->
<bean id="employee" 
      class="com.ram.model.Employee" 
      autowire="byName" />

3. Loading and Running in Java

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");

Employee emp = (Employee) context.getBean("employee");
emp.display();

Key Takeaway

autowire="byName" provides an intuitive, convention-over-configuration mechanism for XML dependency injection. As long as your bean identifiers align with property names, Spring handles the injection effortlessly while reducing repetitive XML configuration.

Recommended Auto-Wiring Tutorials from Ram N Java

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What is byName Auto-wiring mode in Spring?

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0%20http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.ram.core</groupId>

    <artifactId>SpringDemo</artifactId>

    <packaging>jar</packaging>

    <version>1.0-SNAPSHOT</version>

    <name>SpringDemo</name>

    <url>http://maven.apache.org</url>

    <properties>

        <spring.version>5.0.2.RELEASE</spring.version>

    </properties>

    <dependencies>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <!-- Spring 5 dependencies -->

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-core</artifactId>

            <version>${spring.version}</version>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>${spring.version}</version>

        </dependency>

    </dependencies>

</project>

Address.java

package com.ram.model;

public class Address

{

    private String city;

    private String state;

    private String country;

    public Address(String city, String state, String country)

    {

        this.city = city;

        this.state = state;

        this.country = country;

    }

    @Override

    public String toString()

    {

        return "Address [city=" + city + ", state=" + state + ", country="

                + country + "]";

    }

}

Employee.java

package com.ram.model;

public class Employee

{

    private int id;

    private String name;

    private Address address;

    public int getId()

    {

        return id;

    }

    public void setId(int id)

    {

        this.id = id;

    }

    public String getName()

    {

        return name;

    }

    public void setName(String name)

    {

        this.name = name;

    }

    public Address getAddress()

    {

        return address;

    }

    public void setAddress(Address address)

    {

        this.address = address;

    }

    public void displayEmployeeDetails()

    {

        System.out.println("Employee [id=" + id + ", name=" + name

                + ", address=" + address + "]");

    }

}

applicationContext.xml

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

http://www.springframework.org/schema/beans/spring-beans-4.3.xsd">

    <bean id="address" class="com.ram.model.Address">

        <constructor-arg value="Chennai"></constructor-arg>

        <constructor-arg value="Tamil Nadu"></constructor-arg>

        <constructor-arg value="India"></constructor-arg>

    </bean>

    <bean id="employee" class="com.ram.model.Employee" autowire="byName">

        <property name="id" value="100"></property>

        <property name="name" value="Peter"></property>

    </bean>

</beans>

App.java

package com.ram.core;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import com.ram.model.Employee;

public class App

{

    public static void main(String[] args)

    {

        ApplicationContext context = new ClassPathXmlApplicationContext(

                "applicationContext.xml");

        System.out.println("---------------------------------------");

        Employee employee = (Employee) context.getBean("employee");

        System.out.println(

                "Got employee object from the ApplicationContext[Spring Container]");

        employee.displayEmployeeDetails();

    }

}

Output

Jun 28, 2018 9:25:58 AM org.springframework.context.support.AbstractApplicationContext prepareRefresh

INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@5b37e0d2: startup date [Thu Jun 28 09:25:58 IST 2018]; root of context hierarchy

Jun 28, 2018 9:25:58 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions

INFO: Loading XML bean definitions from class path resource [applicationContext.xml]

---------------------------------------

Got employee object from the ApplicationContext[Spring Container]

Employee [id=100, name=Peter, address=Address [city=Chennai, state=Tamil Nadu, country=India]]